As of Alpha 9, Large Tv had disappeared from the Objects Menu, and it is no longer possible to buy it. However, Large Tv still can be dismantled and placed, and prisoners will use it to lower their needs.
The Large TV is a bigger version of the Tv, it's twice the size. As of Alpha-7, Large TV's sprite is fixed and it now also lowers Comfort and Recreation needs.
In the full release, the The Large TV can be found in campaign mission 3 (G.A.B.O.S).
In beta v2, a 7x7 square before the TV lowers the recreation need for prisoners. They can do other things, while being there, just like the TV. It is also buyable again.